The majority of towel and tissue products are presently manufactured according to one of either the conventional wet pressing (CWP) or through-air drying (TAD) processes. In the CWP process, water is removed from the nascent web by mechanical pressure and the resulting sheet is dry embossed. A disadvantage of this process is that it densifies the web, decreasing bulk and absorbency in the resultant sheet. The TAD process is frequently preferred for the manufacture of tissue and similar cellulosic based absorbent products because it avoids the compressive forces of the dewatering step in the CWP method. In the TAD process, the wet web is formed by depositing a papermaking furnish onto a moving forming fabric where it is initially drained, and then transferring the resulting very wet web onto a TAD fabric, which is generally of a very open and permeable design. The TAD fabric is directed around a permeable drum where the sheet is non-compressively dried by passing hot air through the drum and web while it is held in intimate contact with the fabric. The product may then pass over a subsequent Yankee dryer, which is essentially a large steam cylinder with a polished surface, or the Yankee may be omitted. Through-air dryers may be used either before or after a Yankee dryer to preserve bulk and increase drying efficiency. It is well known that fabrics having a three-dimensional (i.e. non-planar) product side (PS) surface can introduce protuberances into the sheet which can, in turn, impart significantly increased bulk and absorbent capacity to the resulting paper product. The efficiency of the TAD process can be significantly enhanced through the use of single layer, high air permeability fabrics.
A TAD fabric should ideally have sufficient open area to provide the required air flow to the paper web so as to promote efficient drying. The fabric should also have a sufficiently high contact area on its PS to ensure successful transfer of the sheet from the TAD to subsequent dryer elements, such as a Yankee cylinder. Fabrics intended for this purpose and which impart a machine direction (MD) oriented pattern in the sheet are generally preferred over those which create a generally cross-machine direction (CD) oriented pattern because this provides the sheet with a smoother “feel”, which is desirable in consumer oriented products such as tissue, towel and similar absorbent products. An MD oriented pattern in the sheet will require longer MD oriented yarn “floats” in the PS, i.e. areas in the fabric where the MD oriented yarns are not bound by the CD yarns. Fabric weave patterns which provide long MD oriented floats will generally also provide higher air permeabilities than patterns which do not.